Photosensors or photodetectors are sensors that detect light or other electromagnetic energy. There are several varieties of photosensors or photodetectors, many of which are manufactured using conventional CMOS technologies. For example, photosensors or photodetectors can be active pixel sensors (APS) commonly used in cellular telephone cameras, web cameras, and even some digital single-lens reflex (DSLR) cameras. These type of image sensors have emerged as an alternative to charge-coupled device (CCD) sensors.
Many types of photosensors or photodetectors implement CMOS integrated nanophotonics circuits. These nanophotonics circuits include crystalline materials like germanium or III-V compounds, which are desirable for use as the active element in photodetector components. This is due to their high quantum efficiency. In the manufacturing process, the crystalline materials are encapsulated in order to protect the crystalline structure from other manufacturing processes.
Using liquid phase epitaxy, amorphous or polycrystalline films (e.g., germanium or III-V compounds) can be deposited at low temperatures in an amorphous or polycrystalline state, and then crystallized thermally. This technique provides for a high degree of integration flexibility. During the crystallization anneal, though, the amorphous or polycrystalline material (e.g., Ge) expands and contracts, creating stress on the encapsulation films. This stress can create a breach in the encapsulation, resulting in defects that can subsequently degrade the operation of the photodetector. For example, Ge recrystallization anneal creates stress points which penetrate the encapsulation structure breaching the integrity of the encapsulation and leaking Ge out of the structure. The main defect type is the removal of Ge during silicide formation by the wet cleans that access the Ge through the breach in the encapsulation.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.